vue 报错：Cannot read property '__ob__' of undefined

My reasons: after the introduction of the component is not registered

<script>
  import ComFirst from "../../components/ComFirst.vue"
  import ComSecond from "../../components/ComSecond.vue"

  export default {
    name: 'VueFirst',
    data() {
      return {}
    },
    Components: {    // << This step is not done
      ComFirst,
      ComSecond
    },
  }
</script>